Solution to task 457 from Chertov´s for extramural stud

Solution to task 457 from Chertov´s for extramural stud

457. A loop, in which a constant current strength I = 60 A is maintained, is freely established in a uniform magnetic field (B = 20 mT). The diameter of the coil is d = 10 cm. What work A needs to be done in order to rotate the coil about the axis coinciding with the diameter by the angle α = π / 3?